Stimulus contributions to operant resurgence

In two experiments, pigeons were exposed to a three‐phase resurgence procedure (train Response A; extinguish Response A and train Response B; extinguish Response B). In the first experiment, the stimuli associated with phases were different, resulting in a resurgence procedure combined with an ABC renewal procedure. Presenting the novel stimulus, C, during extinction of both responses in the third phase resulted in minimal resurgence. Subsequently, substituting the original training Stimulus A for Stimulus C resulted in resurgence with all pigeons. In the second experiment, resurgence with the same stimuli present in all three phases of the resurgence procedure (AAA) was compared concurrently with a resurgence procedure in which the ABC renewal procedure used in Experiment 1 was superimposed. Substantially more resurgence occurred with the AAA procedure compared to the ABC procedure. Although ABC renewal in combination with the resurgence procedure generated some resurgence, such recurrent responding was attenuated relative to that observed when the stimulus conditions were constant across phases. Combined with earlier research showing the enhancing effects of combining resurgence and ABA renewal procedures, the present results elaborate on how stimuli correlated with certain behavioral histories affect the course of operant resurgence.     

An immediate-shock freezing deficit with discrete cues: a possible role for unconditioned stimulus processing mechanisms.

Five experiments with C57BL/6 mice (Mus musculus) investigated whether failures in shock processing might contribute to deficits in freezing that occur after an animal receives a shock immediately on exposure to a conditioning context. Experiment 1 found that more contextual freezing resulted from delayed shocks than from immediate shocks across 4 shock intensities. Experiment 2 extended the immediate-shock freezing deficit to discrete stimuli. Experiment 3 found that preexposure to the to-be-conditioned cue did not facilitate immediate cued conditioning. Experiment 4 found that context preexposure enhanced context-evoked fear after an immediate shock. Experiment 5 found that context preexposure also enhanced immediate cued conditioning. These findings are problematic for current theories of the immediate-shock freezing deficit that focus exclusively on processing of the conditioned stimulus, and they suggest that failures in shock processing may contribute to the deficit.     

Resurgence of temporal patterns of responding

The resurgence of temporal patterns of key pecking by pigeons was investigated in two experiments. In Experiment 1, positively accelerated and linear patterns of responding were established on one key under a discrete-trial multiple fixed-interval variable-interval schedule. Subsequently, only responses on a second key produced reinforcers according to a variable-interval schedule. When reinforcement on the second key was discontinued, positively accelerated and linear response patterns resurged on the first key, in the presence of the stimuli previously correlated with the fixed- and variable-interval schedules, respectively. In Experiment 2, resurgence was assessed after temporal patterns were directly reinforced. Initially, responding was reinforced if it approximated an algorithm-defined temporal pattern during trials. Subsequently, reinforcement depended on pausing during trials and, when it was discontinued, resurgence of previously reinforced patterns occurred for each pigeon and for 2 of 3 pigeons during a replication. The results of both experiments demonstrate the resurgence of temporally organized responding and replicate and extend previous findings on resurgence of discrete responses and spatial response sequences.     

Is an epigenetic switch the key to persistent extinction?

Many studies of learning have demonstrated that conditioned behavior can be eliminated when previously established relations between stimuli are severed. This extinction process has been extremely important for the development of learning theories and, more recently, for delineating the neurobiological mechanisms that underlie memory. A key finding from behavioral studies of extinction is that extinction eliminates behavior without eliminating the original memory; extinguished behavior often returns with time or with a return to the context in which the original learning occurred. This persistence of the original memory after extinction creates a challenge for clinical applications that use extinction as part of a treatment intervention. Consequently, a goal of recent neurobiological research on extinction is to identify potential pharmacological targets that may result in persistent extinction. Drugs that promote epigenetic changes are particularly promising because they can result in a long-term molecular signal that, combined with the appropriate behavioral treatment, can cause persistent changes in behavior induced by extinction. We will review evidence demonstrating extinction enhancements by drugs that target epigenetic mechanisms and will describe some of the challenges that epigenetic approaches face in promoting persistent suppression of memories.     

An analysis of reinforcement history effects

Four pigeons were exposed to two tandem variable-interval differential-reinforcement-of-low-rate schedules under different stimulus conditions. The values of the tandem schedules were adjusted so that reinforcement rates in one stimulus condition were higher than those in the other, even though response rates in the two conditions were nearly identical. Following this, a fixed-interval schedule of either shorter or longer values than, or equal to the baseline schedule, was introduced in the two stimulus conditions respectively. Response rates during those fixed-interval schedules typically were higher in the presence of the stimuli previously correlated with the lower reinforcement rates than were those in the presence of the stimuli previously correlated with the higher reinforcement rates. Such effects of the reinforcement history were most prominent when the value of the fixed-interval schedule was shorter. The results are consistent with both incentive contrast and response strength conceptualizations of related effects. They also suggest methods for disentangling the effects of reinforcement rate on subsequent responding, from the response rate with which it is confounded in many conventional schedules of reinforcement.     

Unsignaled delay of reinforcement, relative time, and resistance to change

Two experiments with pigeons examined the effects of unsignaled, nonresetting delays of reinforcement on responding maintained by different reinforcement rates. In Experiment 1, 3-s unsignaled delays were introduced into each component of a multiple variable-interval (VI) 15-s VI 90-s VI 540-s schedule. When considered as a proportion of the preceding immediate reinforcement baseline, responding was decreased similarly for the three multiple-schedule components in both the first six and last six sessions of exposure to the delay. In addition, the relation between response rates and reinforcement rates was altered such that both parameters of the single-response version of the matching law (i.e., k and Re) were decreased. Experiment 2 examined the effects of unsignaled delays ranging from 0.5 s to 8.0 s on responding maintained by a multiple VI 20-s VI 120-s schedule of reinforcement. Response rates in both components increased with brief unsignaled delays and decreased with longer delays. As in Experiment 1, response rates as a proportion of baseline were affected similarly for the two components in both the first six and last six sessions of exposure to the delay. Unlike delays imposed between two stimulus events, the effects of delays between responses and reinforcers do not appear to be attenuated when the average time between reinforcers is longer. In addition, the disruptions produced by unsignaled delays appear to be inconsistent with the general finding that responding maintained by higher rates of reinforcement is less resistant to change.     

Variable-interval schedule performance in open and closed economies

In two experiments, pigeons obtained food according to variable-interval schedules. In the first experiment, equivalent variable-interval schedules with average interreinforcer intervals ranging between 10 and 80 s in different conditions were studied in both open and closed economies. Response rates increased as reinforcement frequency decreased in the closed economy. By contrast, in the open economy response rates decreased for 1 bird and were variable for the other as reinforcement frequency decreased. The second experiment showed that the differences in the functions between responding and reinforcement frequency in the two types of economies were not due to changes in deprivation level. These results suggest that open and closed economies yield different behavioral effects. This conclusion is supported further by a reconsideration of previous findings that appear counter to the conclusion.     

What is happening in psychology of learning courses?

Current practices in the undergraduate Psychology of Learning course were assessed through a survey in which a questionnaire probing the teaching of the course was sent to 238 4-year colleges and universities in the United States. Fifty-four percent of the questionnaires were returned. Learning courses were taught at all but 10 of the schools that responded. The course typically is one of several that can be selected to fulfill requirements for the major in psychology. The course orientation and content varied widely from cognitive to eclectic to behavioral, and laboratory requirements existed in less than half of the courses. The effects of these practices on behavior analysis are considered and several suggestions are made for teaching behavior analysis in the Learning course and elsewhere to undergraduates.